Integrated circuit devices are widely used in consumer and commercial applications. As the integration density of integrated circuits continues to increase, more active devices such as transistors are integrated in an integrated circuit substrate. These active devices are selectively interconnected using a metal wiring layer on the integrated circuit.
The metal wiring layer may impact the performance and reliability of the integrated circuit device. In particular, the metal wiring layer may be subject to electromigration, thereby degrading the metal wiring layer. It is known that the reliability of the metal wiring layer can be increased by increasing the mean grain size of the metal wiring layer, by reducing deviations in the mean grain size and by growing the metal wiring layer to have a predetermined crystallographic orientation. Finally, the surface morphology of the metal wiring layer can also determine the performance and reliability of the metal wiring layer.
Aluminum is widely used as a metal wiring layer in integrated circuits. In fabricating aluminum wiring layers, it is known that the (111) crystal orientation can provide improved electromigration resistance. See, for example, a publication by Shibata et al. entitled "The Effects of the Al(111) Crystal Orientation on Electromigration in Half-Micron Layered Al Interconnects", Japan Journal of Applied Physics, Vol. 32, 1993, pp. 4479-4484. As disclosed therein, it was found that Al(111) preferred orientation is strongly dependent on the crystal structure and process sequence of the under-metal and universally determined by the difference between the spacing of Al(111) plane and under-metal planes. Moreover, it was found that the electromigration endurance tends to improve in proportion to the degree of Al(111) preferred orientation.
It has also been found that a (111) crystal orientation of an aluminum layer can improve the life span of the layer. See, for example, a publication by Onoda et al., entitled "Al-Si Crystallographic Orientation Transition in Al-Si/TiN Layered Structures and Electromigration Performance as Interconnects", Journal of Applied Physics, Vol. 77, No.2, Jan. 15, 1995, pp. 885-892. As disclosed therein, the electromigration lifetime is longer in Al metal lines having a large grain size, a small grain size standard deviation and a strong (111) orientation.
Finally, it is also known that insulator surface roughness can effect the electromigration properties and surface morphology of an aluminum alloy layer. See, for example, an article by Onoda et al. entitled "Effects of Insulator Surface Roughness of Al-Alloy Film Properties and Electromigration Performance in Al-Alloy/Ti Insulator Layered Interconnects", J. Vac. Sci. Technol. B, Vol. 14, No. 4, Jul./Aug. 1996, pp. 2645-2655. Similar effects may be found for metal wiring structures other than aluminum. See, for example, a publication by Hashimoto et al. entitled "Bias-Induced Structure Transition in Reactively Sputtered TiN Filrs", Applied Physics Letters, Vol. 54, No. 2, 1989, pp. 120-122. This publication discloses that a crystallographic structure transition in TiN films may be observed with an increase in negative substrate bias and reactive sputtering. The crystal orientation normal to the film surface changed from (111) to (200) direction.
Unfortunately, it may be difficult to form a metal wiring structure having a preferred crystal orientation. More specifically, a metal wiring structure may include an underlying wetting layer, such as titanium or titanium nitride. Since the wetting layer may have multiple crystal orientations, it may be difficult to form a metal wiring layer thereon with a preferred crystal orientation. Therefore, the electromigration resistance, reliability and surface morphology of the metal wiring layer may be degraded.